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Transplantation of genetically corrected autologous hematopoietic stem cells is an attractive approach for the cure of sickle-cell disease and beta-thalassemia. Here,we infected human cord blood cells with a self-inactivating lentiviral vector encoding an anti-sickling betaA-T87Q-globin transgene and analyzed the transduced progeny produced over a 6-month period after transplantation of the infected cells directly into sublethally irradiated NOD/LtSz-scid/scid mice. Approximately half of the human erythroid and myeloid progenitors regenerated in the mice containing the transgene,and erythroid cells derived in vitro from these in vivo-regenerated cells produced high levels of betaA-T87Q-globin protein. Linker-mediated PCR analysis identified multiple transgene-positive clones in all mice analyzed with 2.1 +/- 0.1 integrated proviral copies per cell. Genomic sequencing of vector-containing fragments showed that 86% of the proviral inserts had occurred within genes,including several genes implicated in human leukemia. These findings indicate effective transduction of very primitive human cord blood cells with a candidate therapeutic lentiviral vector resulting in the long-term and robust,erythroid-specific production of therapeutically relevant levels of beta-globin protein. However,the frequency of proviral integration within genes that regulate hematopoiesis points to a need for additional safety modifications. View Publication

Most polyreactive and antinuclear antibodies are removed from the human antibody repertoire during B cell development. To elucidate how B cell receptor (BCR) signaling may regulate human B cell tolerance,we tested the specificity of recombinant antibodies from single peripheral B cells isolated from patients suffering from X-linked agammaglobulinemia (XLA). These patients carry mutations in the Bruton's tyrosine kinase (BTK) gene that encode an essential BCR signaling component. We find that in the absence of Btk,peripheral B cells show a distinct antibody repertoire consistent with extensive secondary V(D)J recombination. Nevertheless,XLA B cells are enriched in autoreactive clones. Our results demonstrate that Btk is essential in regulating thresholds for human B cell tolerance. View Publication

Acute myeloid leukemia (AML) cells are characterized by a constitutive and abnormal activation of the nuclear factor-kappaB (NF-kappaB) transcription factor. This study,conducted in vitro on 18 patients,shows that targeting the IKB kinase 2 (IKK2) kinase with the specific pharmacologic inhibitor AS602868 to block NF-kappaB activation led to apoptosis of human primary AML cells. Moreover,AS602868 potentiated the apoptotic response induced by the current chemotherapeutic drugs doxorubicin,cytarabine,or etoposide (VP16). AS602868-induced cell death was associated with rupture of the mitochondrial transmembrane potential and activation of cellular caspases. NF-kappaB inhibition did not affect normal CD34+ hematopoietic precursors,suggesting that it could represent a new adjuvant strategy for AML treatment. View Publication

A new entity of acute leukemia coexpressing CD4(+)CD56(+) markers without any other lineage-specific markers has been identified recently as arising from lymphoid-related plasmacytoid dendritic cells (pDCs). In our laboratory,cells from a patient with such CD4(+)CD56(+) lineage-negative leukemia were unexpectedly found to also express the myeloid marker CD33. To confirm the diagnosis of pDC leukemia despite the CD33 expression,we demonstrated that the leukemic cells indeed exhibited pDC phenotypic and functional properties. In 7 of 8 other patients with CD4(+)CD56(+) pDC malignancies,we were able to confirm that the tumor cells expressed CD33 although with variable expression levels. CD33 expression was shown by flow cytometry,reverse transcriptase-polymerase chain reaction,and immunoblot analysis. Furthermore,CD33 monoclonal antibody stimulation of purified CD4(+)CD56(+) leukemic cells led to cytokine secretion,thus confirming the presence of a functional CD33 on these leukemic cells. Moreover,we found that circulating pDCs in healthy individuals also weakly express CD33. Overall,our results demonstrate that the expression of CD33 on CD4(+)CD56(+) lineage-negative cells should not exclude the diagnosis of pDC leukemia and underline that pDC-specific markers should be used at diagnosis for CD4(+)CD56(+) malignancies. View Publication

Leukocyte trafficking to sites of inflammation follows a defined temporal pattern,and evidence suggests that initial neutrophil transendothelial migration modifies endothelial cell phenotype. We tested the hypothesis that preconditioning of human umbilical vein endothelial cells (HUVEC) by neutrophils would also modify the subsequent transendothelial migration of T lymphocytes across cytokine-stimulated HUVEC in an in vitro flow assay. Using fluorescence microscopy,preconditioning of HUVEC by neutrophils was observed to significantly reduce the extent of subsequent stromal cell-derived factor-1alpha (SDF-1alpha [CXCL12])-mediated T lymphocyte transendothelial migration,without reducing accumulation. In contrast,recruitment of a second wave of neutrophils was unaltered. Conditioned medium harvested after transendothelial migration of neutrophils or supernatants from stimulated neutrophils mediated a similar blocking effect,which was negated using a specific neutrophil elastase inhibitor. Furthermore,T lymphocyte transendothelial migration was inhibited by treatment of HUVEC with purified neutrophil elastase,which selectively cleaved the amino terminus of HUVEC-bound SDF-1alpha,which is required for its chemotactic activity. The reduction in T lymphocyte transendothelial migration was not observed using a different chemokine,ELC (CCL19),and was not reversed by replenishment of SDF-1alpha,indicating endothelial retention of the inactivated chemokine. In summary,transmigrating neutrophils secrete localized elastase that is protected from plasma inhibitors,and thereby modulate trafficking of other leukocyte subsets by altering the endothelial-associated chemotactic activities. View Publication

Virus-specific CD8(+) T cells are associated with declining viremia in acute human immunodeficiency virus (HIV)1 infection,but do not correlate with control of viremia in chronic infection,suggesting a progressive functional defect not measured by interferon gamma assays presently used. Here,we demonstrate that HIV-1-specific CD8(+) T cells proliferate rapidly upon encounter with cognate antigen in acute infection,but lose this capacity with ongoing viral replication. This functional defect can be induced in vitro by depletion of CD4(+) T cells or addition of interleukin 2-neutralizing antibodies,and can be corrected in chronic infection in vitro by addition of autologous CD4(+) T cells isolated during acute infection and in vivo by vaccine-mediated induction of HIV-1-specific CD4(+) T helper cell responses. These data demonstrate a loss of HIV-1-specific CD8(+) T cell function that not only correlates with progressive infection,but also can be restored in chronic infection by augmentation of HIV-1-specific T helper cell function. This identification of a reversible defect in cell-mediated immunity in chronic HIV-1 infection has important implications for immunotherapeutic interventions. View Publication

Cell-to-cell virus transmission is one of the most efficient mechanisms of human immunodeficiency virus (HIV) spread,requires CD4 and coreceptor expression in target cells,and may also lead to syncytium formation and cell death. Here,we show that in addition to this classical coreceptor-mediated transmission,the contact between HIV-producing cells and primary CD4 T cells lacking the appropriate coreceptor induced the uptake of HIV particles by target cells in the absence of membrane fusion or productive HIV replication. HIV uptake by CD4 T cells required cellular contacts mediated by the binding of gp120 to CD4 and intact actin cytoskeleton. HIV antigens taken up by CD4 T cells were rapidly endocytosed to trypsin-resistant compartments inducing a partial disappearance of CD4 molecules from the cell surface. Once the cellular contact was stopped,captured HIV were released as infectious particles. Electron microscopy revealed that HIV particles attached to the surface of target cells and accumulated in large (0.5-1.0 microm) intracellular vesicles containing 1-14 virions,without any evidence for massive clathrin-mediated HIV endocytosis. The capture of HIV particles into trypsin-resistant compartments required the availability of the gp120 binding site of CD4 but was independent of the intracytoplasmic tail of CD4. In conclusion,we describe a novel mechanism of HIV transmission,activated by the contact of infected and uninfected primary CD4 T cells,by which HIV could exploit CD4 T cells lacking the appropriate coreceptor as an itinerant virus reservoir. View Publication

Hematopoietic progenitor/stem cell homing to the bone marrow requires the concerted action of several adhesion molecules. Endothelial P- and E-selectins play an important role in this process,but their ligands on a large subset of neonate-derived human CD34+ cells are absent,leading to a reduced ability to interact with the bone marrow (BM) microvasculature. We report here that this deficiency results from reduced alpha1,3-fucosyltransferase (FucT) expression and activity in these CD34+ cells. Incubation of CD34+ cells with recombinant human FucTVI rapidly corrected the deficiency in nonbinding CD34+ cells and further increased the density of ligands for both P- and E-selectins on all cord blood-derived CD34+ cells. Intravital microscopy studies revealed that these FucTVI-treated CD34+ cells displayed a marked enhancement in their initial interactions with the BM microvasculature,but unexpectedly,homing into the BM was not improved by FucTVI treatment. These data indicate that,although exogenous FucT enzyme activity can rapidly modulate selectin binding avidity of cord blood CD34+ cells,further studies are needed to understand how to translate a positive effect on progenitor cell adhesion in bone marrow microvessels into one that significantly influences migration and lodgement into the parenchyma. View Publication

NK cells play a critical role in the rejection of xenografts. In this study,we report on an investigation of the effect of complement regulatory protein,a decay accelerating factor (DAF: CD55),in particular,on NK cell-mediated cytolysis. Amelioration of human NK cell-mediated pig endothelial cell (PEC) and pig fibroblast cell lyses by various deletion mutants and point substitutions of DAF was tested,and compared with their complement regulatory function. Although wild-type DAF and the delta-short consensus repeat (SCR) 1-DAF showed clear inhibition of both complement-mediated and NK-mediated PEC lyses,delta-SCR2-DAF and delta-SCR3-DAF failed to suppress either process. However,delta-SCR4-DAF showed a clear complement regulatory effect,but had no effect on NK cells. Conversely,the point substitution of DAF (L147 x F148 to SS and KKK(125-127) to TTT) was half down-regulated in complement inhibitory function,but the inhibition of NK-mediated PEC lysis remained unchanged. Other complement regulatory proteins,such as the cell membrane-bound form factor H,fH-PI,and C1-inactivator,C1-INH-PI,and CD59 were also assessed,but no suppressive effect on NK cell-mediated PEC lysis was found. These data suggest,for DAF to function on NK cells,SCR2-4 is required but no relation to its complement regulatory function exists. View Publication

NK cells protect hosts against viral pathogens and transformed cells,and dendritic cells (DCs) play important roles in activating NK cells. We now find that murine IL-15Ralpha-deficient DCs fail to support NK cell cytolytic activity and elaboration of IFN-gamma,despite the fact that these DCs express normal levels of costimulatory molecules and IL-12. By contrast,IL-15Ralpha expression on NK cells is entirely dispensable for their activation by DCs. In addition,blockade with anti-IL-15Ralpha and anti-IL-2Rbeta but not anti-IL-2Ralpha-specific Abs prevents NK cell activation by wild-type DCs. Finally,presentation of IL-15 by purified IL-15Ralpha/Fc in trans synergizes with IL-12 to support NK cell priming. These findings suggest that murine DCs require IL-15Ralpha to present IL-15 in trans to NK cells during NK cell priming. View Publication

Mixed chimaerism and graft rejection are higher after reduced-intensity allogeneic stem cell transplantation (RIST) with T-cell depleted (TCD) allografts. As host immune status before RIST affects engraftment,we hypothesized that targeted depletion of host lymphocytes prior to RIST would abrogate graft rejection and promote donor chimaerism. Lymphocyte-depleting chemotherapy was administered at conventional doses to subjects prior to RIST with the intent of decreasing CD4(+) counts to textless0.05 x 10(9)cells/l. Subjects (n = 18) then received reduced-intensity conditioning followed by ex vivo TCD human leucocyte antigen-matched sibling allografts. All evaluable patients (n = 17) were engrafted; there were no late graft failures. At day +28 post-RIST,12 patients showed complete donor chimaerism. Mixed chimaerism in the remaining five patients was associated with higher numbers of circulating host CD3(+) cells (P = 0.0032) after lymphocyte-depleting chemotherapy and was preferentially observed in T lymphoid rather than myeloid cells. Full donor chimaerism was achieved in all patients after planned donor lymphocyte infusions. These data reflect the importance of host immune status prior to RIST and suggest that targeted host lymphocyte depletion facilitates the engraftment of TCD allografts. Targeted lymphocyte depletion may permit an individualized approach to conditioning based on host immune status prior to RIST. View Publication

Thrombopoietin (Tpo) is the primary cytokine regulating megakaryocyte development and platelet production. Tpo signaling through its receptor,c-mpl,activates multiple pathways including signal transducer and activator of transcription (STAT)3,STAT5,phosphoinositide 3-kinase-Akt,and p42/44 mitogen-activated protein kinase (MAPK). The adaptor protein Lnk is implicated in cytokine receptor and immunoreceptor signaling. Here,we show that Lnk overexpression negatively regulates Tpo-mediated cell proliferation and endomitosis in hematopoietic cell lines and primary hematopoietic cells. Lnk attenuates Tpo-induced S-phase progression in 32D cells expressing mpl,and Lnk decreases Tpo-dependent megakaryocyte growth in bone marrow (BM)-derived megakaryocyte culture. Consistent with this result,we found that in both BM and spleen,Lnk-deficient mice exhibited increased numbers of megakaryocytes with increased ploidy compared with wild-type mice. In addition,Lnk-deficient megakaryocytes derived from BM and spleen showed enhanced sensitivity to Tpo during culture. The absence of Lnk caused enhanced and prolonged Tpo induction of STAT3,STAT5,Akt,and MAPK signaling pathways in CD41+ megakaryocytes. Furthermore,the Src homology 2 domain of Lnk is essential for Lnk's inhibitory function. In contrast,the conserved tyrosine near the COOH terminus is dispensable and the pleckstrin homology domain of Lnk contributes to,but is not essential for,inhibiting Tpo-dependent 32D cell growth or megakaryocyte development. Thus,Lnk negatively modulates mpl signaling pathways and is important for Tpo-mediated megakaryocytopoiesis in vivo. View Publication